In general, a thermoelectric material is a material capable of being utilized in active cooling, waste heat generation, and the like, using a Peltier effect and a Seebeck effect. The Peltier effect is a phenomenon that when a direct-current (DC) voltage is applied from the outside, holes of a p-type material and electrons of an n-type material are moved to generate heat generation and heat absorption at both ends of the material. The Seebeck effect is a phenomenon that when heat is supplied from an external heat source, the holes and the electrons are moved to generate a current flow in the material, thereby resulting in electricity generation.
It is recognized that the active cooling using the thermoelectric material as described above improves thermal stability of devices, does not generate vibration and noise, and does not use separate condensers and refrigerants to have a small volume and to be environmentally friendly. The active cooling using the thermoelectric material as described above may be used in a refrigerant-free refrigerator, air conditioner, and various micro-cooling systems, and the like, in particular, when a thermoelectric device is attached to various memory devices, as compared to the existing cooling schemes, the thermoelectric device may decrease volume and maintain the device at an uniform and stable temperature, thereby improving performance of the device.
Meanwhile, when the thermoelectric material is utilized for thermoelectric generation by the Seebeck effect, waste heat is capable of being utilized as an energy source to increase efficiency of energy such as waste heat of car engine and exhaust system, waste incinerator and steel mill, power supply of medical device in a human body using a human heat, and the like, or to be capable of being applied in various fields in which the waste heat is collected and used.
As a factor measuring performance of the thermoelectric material as described above, a dimensionless thermoelectric figure of merit (ZT) value is used. In order to increase the ZT value, a material having a high Seebeck coefficient and high electric conductivity, and a low thermal conductivity is required.
It is known that the existing indium selenide thermoelectric material has high ZT value due to a low thermal conductivity and a high Seebeck coefficient (Applied Physics Letters vol. 95, p. 212106, 2009/Nature vol. 459, p. 965, 2009). In addition, as being verified in many thermoelectric materials such as Bi2Te3, and the like, when nanoparticles are dispersed, a thermal conductivity is decreased due to phonon scattering on an interface of the nanoparticle (J. electronic Materials vol. 41, 1165, 2012/Physical Review Letters vol. 96, 045901, 2006). However, when effective metal nanoparticles are dispersed into Bi2Te3, and the like, there are problems in that the preparation is not easy due to limitation in a synthetic temperature, there is a limitation in workable temperature thereof due to thermal instability of the nanoparticle, and when the nanoparticles are exposed to heat for a long time, thermal stability of the nanoparticle is rapidly deteriorated to decrease performance.